1. Field of the Invention
The present invention relates in general to an automotive meter, such as speedometer, tachometer or the like, and more particularly, to automotive meters of a type which is equipped with a dial board illuminating device.
2. Description of the Prior Art
In order to clarify the present invention, two conventional automotive speedometers of the above-mentioned type are described with reference to the accompanying drawings.
In FIG. 2, there is shown one conventional speedometer of a so-called "back lamp" type. The meter comprises a transparent base plate 1 constructed of acrylate resin or the like, an opaque film 3 attached to a front surface of the base plate 1 and an electric lamp 4 positioned behind the base plate 1. The opaque film 3 has graduations 2 cut out therefrom. The base plate 1 and the graduated opaque film 3 thus constitute a so-called "dial board". Although not shown in the drawing, a pointer is arranged in front of the dial board. Upon energization, the lamp 4 produces visible light rays which pass through the cut out graduations 2 from the back of the base plate 1. With this, the graduations are clearly viewed from the front of the meter particularly in surroundings which receive little light.
In FIG. 3, there is shown another conventional speedometer of the so-called "front lamp" type. The meter comprises an opaque base plate 5 and an electric lamp 4 positioned in front of the base plate 5. Graduations 6 are printed on a front surface of the base plate 5 using colored paint, colored ink or the like. The base plate 5 thus graduated serves as a dial board. Upon energization, the lamp 4 produces visible light rays and, thus, illuminates the graduated front surface of the dial board. Thus, the graduations are easily read by a viewer even in dark surroundings.
However, due to usage of the lamp 4 which emits visible light rays, the above-mentioned conventional speedometers fail to provide the graduations of the dial board with an elegant illumination. Furthermore, due to the nature of the lamp 4 used, uneven illumination tends to occur on the graduated face of the dial board. That is, the graduations located near the lamp 4 are highly illuminated, while the graduations located remotely from the lamp 4 are poorly illuminated.